Electromediators in synthesis of sulfur organic compounds based on hydrogen sulfide and thiols

Full text of DOI:10.1134/S001250081011008X

ISSN 0012ꢀ5008, Doklady Chemistry, 2010, Vol. 435, Part 1, pp. 302–306. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.O. Okhlobystin, A.V. Okhlobystina, E.V. Shinkar’, N.T. Berberova, I.L. Eremenko, 2010, published in Doklady Akademii Nauk, 2010, Vol. 435, No. 3,
pp. 352–356.
CHEMISTRY
Electromediators in Synthesis of Sulfur Organic Compounds
Based on Hydrogen Sulfide and Thiols
a
a
a
A. O. Okhlobystin , A. V. Okhlobystina , E. V. Shinkar’ ,
b
c
N. T. Berberova , and Academician I. L. Eremenko
Received April 19, 2010
DOI: 10.1134/S001250081011008X
Development of new synthetic approaches to the removal of protecting groups, initiation of organic
direct introduction of sulfenyl and alkylsulfenyl rearrangements, synthesis of methyl benzoates, flaꢀ
groups into organic compounds is currently an imporꢀ
tant task because of the wide use of their sulfur derivaꢀ
tives in industry and agriculture [1]. Previously [2, 3],
we showed that the electrochemical oneꢀelectron oxiꢀ
vonoids, anodic oxidation of carboxylates, etc. [5].
Available data on the use of electromediators for oxiꢀ
dative activation of sulfurꢀcontaining molecules are
scarce and fragmentary. In this context, this work deals
with studying organic electromediators (Med) for
dation of H S and RSH (R = Alk) in the reaction with
2
unsaturated and aromatic hydrocarbons leads to orgaꢀ
nosulfur derivatives in quantitative yield. However, the
suggested method is rather energyꢀconsuming, which
activation of H S and RSH (R = Alk, Ar) to radical
2
cations, which is promising for lifting the environꢀ
mental and energetic limitations associated with proꢀ
duction of organosulfur compounds. In addition to
differently substituted aromatic amines, metal comꢀ
plexes with redoxꢀactive ligands, which have been
is caused by high anodic potentials of H S (1.60 V) and
2
aliphatic (aromatic) thiols (1.50–1.80 V).
Inorganic mediator systems have been well studied
4]; however, their use in organic synthesis is limited by
[
their poor solubility in nonaqueous solvents. The use studied for the first time as electromediators, hold a
of organic mediators pertains, as a rule, to the selective special place among selected mediators (Scheme 1).
X
X
X
X2N
NX2
N
H
6
: X = H
7: X = CH3
N
4: X = H
5: X = OCH3
C(CH3)3
X
X
C(CH3)3
C(CH3)3
(
H C) C
•
O
O
Cr
3
3
1
2
3
: X = H
: X = CH3
: X = Br
S
S
S
–
X
O
O
•
•
M
(Bu N)
4
O
X
S
•
X
(
H C) C
3 3
O
1
0: X = H, M = Ni
N
H
11: X = CH , M = Ni
3
C(CH3)3
12: X = H, M = Pt
3: X = CH , M = Pt
8
: X = O
1
9: X = S
3
14
Scheme 1.
a
b
c
Astrakhan State Technical University, ul. Tatishcheva 16, Astrakhan, 414025 Russia
Southern Scientific Center, Russian Academy of Sciences, pr. Chekhova 41, RostovꢀonꢀDon, 344006 Russia
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119991 Russia
302

ELECTROMEDIATORS IN SYNTHESIS OF SULFUR ORGANIC COMPOUNDS
303
Difference between the oxidation potentials of hydrogen sulfide and mediators
Med
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Δ
E
, V 0.68 0.76 0.40 1.15 0.62 1.11 0.80 0.91 0.93 0.92 1.04 0.98 1.06 0.80
Note: ΔE = E – E , where E is the oxidation potential of H S, and E is the oxidation potential of an electromediator.
Med
R
Med
R
2
Complexes 10–14 were synthesized by known proꢀ containing molecules. The selected compounds meet
cedures [6–8]. Electrochemical measurements were the requirements for potential mediators [9]. For the
carried out on a platinum anode versus Ag/AgCl (KCl mediator systems under consideration containing
sat.) in CH CN (CH Cl ) with 0.1 M Bu NClO4 as a Med and H S (RSH) molecules, the decrease in the
3
2
2
4
2
supporting electrolyte by means of IPC Pro and Versaꢀ energy barrier (
E) of the reaction have been calcuꢀ
Δ
STAT 3ꢀ400 potentiostats. Chromatographic analysis
of the synthesized organosulfur compounds was carꢀ
ried out on a Yanaco G3800 gas chromatograph with a
lated (table).
According to the estimated
Δ
E values, the activaꢀ
flame photometric detector. The EPR spectra were tion of sulfurꢀcontaining molecules will entail the
recorded on a Bruker ER 200 DꢀSRC spectrometer largest decrease in energy input in the course of elecꢀ
equipped with an ER 4105 DR double resonator (a trosynthesis when mediator
4 is used and the smallest
working frequency of ~9.5 GHz) and an ER 4111 VT decrease will be achieved in the case of compound
3.
temperature control unit. The electronic absorption An analogous dependence is observed for mediator
spectra were recorded on an SFꢀ103 spectrophotomeꢀ systems based on thiols and thiophenol, which are oxiꢀ
ter in the range 190–1100 nm in a spectroelectroꢀ dized at potentials close to the anodic potential of
chemical cell at 298 K. The IR spectra were recorded hydrogen sulfide: С H SH (1.56 V), C H SH (1.62 V),
2
5
4
9
on an FSM 1201 spectrophotometer in the range 400–
C H SH (1.76 V), C H SH (1.78 V), and C H SH
6
6
13
8
17
5
⎯
1
5000 cm . The GC/mass spectra were recorded on
(
1.80 V).
AN Agilent Technologies 6890N GC System chroꢀ
matograph equipped with an Agilent Technologies
Activation of H S and RSH molecules by electroꢀ
2
5
973N MSD mass selective detector. Xꢀray fluoresꢀ mediators occurs in the stepwise process electron
cence analysis was carried out on an ASEꢀ1 Xꢀray chemical stage
electron with reversible electron
energy dispersive analyzer of sulfur.
transfer at electrochemical stages [10]. The general
At relatively low anodic potentials (0.7–1.0 V), principle of the initiating action of Med in the reacꢀ
electromediators
14 form stable radical cation (or tions with sulfurꢀcontaining molecules in the presence
1–
unstable radical) species capable of oxidizing sulfurꢀ of organic substrates can be represented by Scheme 2.
Pt
Med•
+
RSH•+
H+
–
e
RS•
S
P
RS•
RSSR
Med
RSH
(
R = H, C H , C H , C H , C H , C H ; S is the substrate, P is the reaction product).
2 5 4 9 6 13 8 17 6 5
Scheme 2.
The reaction of hydrogen sulfide (thiols, thiopheꢀ
nol) with electrochemically generated radical cation based on unsaturated and aromatic hydrocarbons with
salts of electromediators led to a decrease in the the participation of H S (RSH) was carried out under
intensity of the initial absorption maxima in the elecꢀ energetically favorable conditions, i.e., at the oxidaꢀ
tronic absorption spectra. For some compounds (
tion potentials of the mediators used.
, and ), the electrochemical reactions are compliꢀ
The reaction of H S with 1ꢀhexene in the presence
The electrosynthesis of organosulfur compounds
1–9
2
1, 4,
6
8
cated by removal of the mediators form the electroꢀ
2
generation cycle since they are involved in parallel of electromediators 1–9 (Med : H
S = 1 : 8) yielded
ꢀhexanethiol (43–88%) and dihexyl disulfide (12–
43%). Depending on the mediator nature, the yields of
2
transformations to produce substituted benzidines,
phenothiazine, or polymerization products.
n
DOKLADY CHEMISTRY Vol. 435
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304
OKHLOBYSTIN et al.
fide (18–90.6%). The reactions of the thiols and
thiophenol with 1ꢀoctene in the presence of aromatic
amines 1–9 also lead to the formation of sulfides
I
, µA
.4
0
0
0
0
30 min
5
min
(
80%) (Scheme 3).
.3
.2
.1
0
+
Med
Med•
+
RS•
RSH
RSH•
H+
–
RSH
•
•
R –CH=CH + RS
RS(CH ) R + RS
1
2
2 2 1
RS•
RSSR
−
0.1
(
R = C H , C H , C H , C H ; R = C H , C H ).
2 5 4 9 6 13 8 17 1 4 9 6 13
−
0.2
−
Scheme 3
The reaction of H S with benzene was carried out
500
0
500
1000
1500
2000
, mV
E
2
under the conditions of electrochemical oxidation of
mediators , and . The yield of thiophenol was
3–36%, which is considerably higher than the yields
afforded by the direct introduction of the sulfenyl radꢀ
ical into the aromatic ring (2–5%) [11].
Fig. 1. Cyclic voltammograms of the products of the reacꢀ
tion of ꢀhexyl mercaptan and 1ꢀhexene in the presence of
mediator (CH Cl , Pt anode, Ag/AgCl, 0.1 M
NBu ClO ).
2,
3,
5
7
n
3
1
4
2
2
4
When the radical cation forms of compounds
8 and
n
ꢀoctanethiol and dioctyl disulfide in the reaction of
9
were used for the oxidation of H S, its reactions with
2
hydrogen sulfide with 1ꢀoctene varied within 45–91%
and 8–42%, respectively. The electrolysis of
nꢀС H SH with 1ꢀhexene in the presence of anodiꢀ
6 13
benzoic acid yielded thiosalicylic acid and the symꢀ
metric aromatic disulfide. The reaction of H S with
2
toluene in the presence of these mediators led to the
formation of a mixture of isomeric thiocresols, benꢀ
cally activated mediators 1–9 at the ratio Med : H S =
2
1
: 20 (Fig. 1) led to dihexyl sulfide and dihexyl disulꢀ zylthiol, and disulfide Ar–S–S–Ar (Scheme 4).
CH3
CH3
CH3
CH SH
2
+
HS•
SH
+
CH3
CH3
CH3
CH3
•
S
S•
Med•
+
SH Med
S S
–
H+
Scheme 4.
To obtain asymmetric products, the reactions of
Special attention in this work was paid to studying
thiols (C H SH, C H SH, C H SH, C H SH) with the properties of new electromediators—metal comꢀ
2
5
4
9
6
13
8
17
benzene, toluene and benzoic acid in the presence of
mediators , and at the molar ratio Med : H S =
: 8 were studied. The reactions yield corresponding
plexes, which are good candidates for electrocatalysts
in organic synthesis [9–11]. Previously, it was shown
2,
3,
5
7
2
1
that transition metal complexes with
ligands are able to activate sulfurꢀcontaining moleꢀ
cules [13, 14]. Among complexes, compounds 10 11,
oꢀquinoid
disulfides and sulfides (Scheme 5).
SR
,
X + RS•
X
and 14 proved to be efficient electromediators. Platiꢀ
num complexes 12 and 13 in the presence of excess
hydrogen sulfide gradually decompose in the course of
electrosynthesis of organosulfur compounds and leave
the reaction zone.
(
X = H, CH , NO , COOH; R = C H , C H , C H , C H ).
3
2
2
5
4
9
6
13
8
17
Scheme 5.
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ELECTROMEDIATORS IN SYNTHESIS OF SULFUR ORGANIC COMPOUNDS
305
Nickel complex 10 is a radical anion salt in which
the ligands are prone to spin–spin exchange. The EPR
spectrum of this compound is a singlet with giso = 2.085
at 300 K (Fig. 2). The salt is stable to the sulfurꢀconꢀ
taining molecules used, but its oxidation generates a
biradical species capable of efficiently oxidizing
hydrogen sulfide, thiols, and thiophenol to correꢀ
sponding radical cations. This is due to the high activꢀ
ity of the dithiolate radical with the lifetime of 15 min
at 298 K. The formation of the unstable biradical form
was detected in the electronic absorption spectra. In
the course of electrolysis of compound 10, the spectrum
shows the bathochromic shift (
λ
700 850 nm), which
→
is evidence of the conversion of the radical anion form
of the complex into the radical form. Hence, complex 3240
3280
3320
3360
3400
3440
3480
, Oe
H
10 can be used for activation of sulfurꢀcontaining molꢀ
ecules. The characteristics of complex 11 and its
behavior in the presence of hydrogen sulfide, thiols,
and thiophenol allowed us to arrive at an analogous
conclusion.
Fig. 2. EPR spectrum of complex 10 at 300 K.
ciency of using chromium and nickel complexes with
The efficiency of complexes 10 and 11 as electroꢀ redoxꢀactive ligands in the reactions with H S and
2
mediators, as compared with aromatic amines
1–9,
RSH (R = Alk, Ar) is caused by the enhancement of
increases owing to the preliminary activation of H2S their mediator function by coordination of the moleꢀ
and RSH molecules at the metal site [15]. For chroꢀ cules to the metal site.
mium complex 14, the coordination of sulfurꢀconꢀ
taining molecules to the metal site is impossible
because of steric hindrance. The oneꢀelectron oxidaꢀ
tion of one of the ligands in the complex leads to the
ACKNOWLEDGMENTS
The work was supported by the Russian Foundaꢀ
tion for Basic Research (project nos. 09–03–00677a,
9–03–12122–ofi–m), the Council for Grants of the
President of the Russian Federation for Support of
Young Scientists (grant no. MKꢀ3044.2009.3), and the
Presidium of the RAS (subprogram “Design of
Molecular Magnetically Active Substances and Mateꢀ
rials”).
o
ꢀbenzoquinone form that oxidizes H S (RSH) and is
2
regenerated to the initial trisꢀoꢀsemiquinolate form.
Electron transfers involve only the ligand environꢀ
ment, and the oxidation state of Ni and Cr in mediaꢀ
tors 10, 11, and 14 remains unaltered in the redox proꢀ
cess.
0
We found that the activation of H S by mediators
2
1
0, 11, and 14 occurs by different mechanisms. In the
oxidation of nickel complexes 10 and 11 with 1,2ꢀbenꢀ
zodithiolate ligands, the active form with respect to
hydrogen sulfide is a biradical system and for chroꢀ
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DOKLADY CHEMISTRY Vol. 435
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2010